More information about the stomach and duodenum

The stomach is divided into three parts: the fundus at the top, the body in the middle and the antrum at the end. There is a sphincter at the upper entrance, where the oesophagus joins, and another at the exit called the pyloric sphincter, where it joins the duodenum. The purpose of the upper sphincter is to prevent stomach contents going back up into the oesophagus. The purpose of the lower sphincter is to prevent large portions of food entering the small bowel, which is relatively narrow.

The secretion of the juices, and the contraction of the muscles are stimulated by the thought, sight, smell and taste of food as well as by the presence of food in the stomach, which is why our tummies rumble when we are hungry. The control of the secretions, and the muscular contraction, is mediated by the vagus nerve, which is part of our autonomic nervous system. Cells near the outlet of the stomach produce a hormone called gastrin, which also acts on the oxyntic cells via the chemical histamine, causing them to increase the production of hydrochloric acid.

The duodenum is a C- shaped tube lying between the stomach and the start of the small intestine. In its middle part there is the opening of a duct which carries the secretions from the pancreas and bile from the liver. The pancreatic secretions (see the pancreas) consist mainly of enzymes such as amylase lipase and protease which dissolve carbohydrates, fats and proteins respectively, while the function of bile is to aid the digestion and transport of fats. Pancreatic secretion is stimulated by the presence of food in the duodenum, while that of bile is aided by the contraction of the gall bladder when we eat food containing fat. (Which is why people with gall bladder disease often suffer pain when they eat fatty food. See the liver).